Over the last couple of years the fastest growing trend in fitness has been the uptake of wearable technology. This range of products are now the biggest sellers for electrical retailers and most early adopters are onto their second, if not, third generation of wearable fitness tracker. Its estimated 68.1 million wearable fitness trackers sold in 2015, and

91.3 million are expected to sell in 2016.

Fitness technology now comes built into our wrist watches, smart phones, ear buds and sunglasses. It provides data about where we are, how far and fast we travel, our sleep quality and even our hydration levels.

Check out Xmetrics. This swim specific tracker is worn on the back of your head and gives you real time audio feedback about your stroke count, kick rate, time between turns and breathing.

And why should humans get all the cool gear? Nuzzle is a wearable GPS and activity tracker for your dog or cat.

One of the latest development in fitness trackers is the ability to get a heart rate reading without the need for a pesky chest strap. This is due to optical technology.

Unlike chest straps, which read the electrical pulses associated with heart beats, optical sensors work by using a light to illuminate the capillaries in your wrist. A sensor then measures how frequently blood pumps past. There are a number of problems with this:

2. Blood flow in your wrist is affected by movement and muscle tension.

3. The ability to measure blood flow with an optical sensor is affected by skin tone and the size, shape and structure of your wrist.

What sort of numbers are we talking?

Testing indicates that optical sensor readings taken at the wrist are about 90% accurate at hearts rates around 80-90bpm, when you are completely still. Not an ideal state for improving your fitness.

Pump the heart rate up to 160bpm and you’re looking at approximately 50% accuracy. Add in movement or use your hands and they bug out completely. Essentially we have a fitness tracker that cant track your fitness activity.

Why do we want to measure heart rate anyway? Heart rate is the simplest way to measure how hard you are working. Knowing how hard you are working is critical to understanding if you are exercising the right way to achieve your goals. For heart rate data to be meaningful we want it to be accurate within +/-5bpm.

While wrist band fitness trackers offer many features, if tracking your heart rate is important to you then you really need to get a chest strap, or you can always revert to the two fingers on your pulse trick.